Cancer currently accounts for approx. 13% of all deaths worldwide. In spite of decades of intense research, cancer remains the second leading cause of death in the highly developed countries, accounting for approx. 25% of the deaths. For many types of cancer, surgery—often in combination with chemotherapy, radiation treatment or hyperthermia—is the mainstay of therapeutic intervention.
A cancer is also referred to as a malignant neoplasm, or a malignant tumour. A neoplasm is an abnormal growth of tissue. Neoplasms are differentiated into benign neoplams, precancerous or in situ neoplasms, and malignant neoplasms. Many but not all neoplasms also form tumours, which are solid or fluid-filled lesions that can be differentiated anatomically from the unaffected tissue. Like neoplasms, tumours may be benign, precancerous, or malignant. In common language as well as in the description of the present invention, however, the term “tumour” may be used synonymously with “malignant tumour”.
The vital prognosis of cancer patients depends upon the stage of the disease when it is first diagnosed. Twenty to thirty percent of the patients suffering from gastrointestinal cancers will develop locoregional recurrence as a unique relapse. Epithelial ovarian tumours also display locoregional evolution when they reach stage III. It was demonstrated several years ago that complete surgical resection is a very important factor for the improvement of the prognosis of the patients. This maximal cytoreduction strategy is part of therapeutic protocols that include systemic or intraperitoneal chemotherapy possibly associated with hyperthermia.
The setup of a curative surgery is a major parameter for the future of the patients. Detection of the totality of tumour nodules and their disseminations is a major point influencing post-surgery prognosis. Differentiation between tumour and normal tissues is not always easy, especially when patients have been given neo-adjuvant treatments. Surgeons are then only guided by their visual and tactile senses, and by their experience; there is no intra-operative technique available at the moment to help them visualise the extensions of the tumour.
It has been suggested that cancer resection surgery may be improved by the use of in situ photodetection. Photodetection relies on the exposure of the potentially affected tissues with a compound having affinity to a tumour and being able to be optically visualised at a selected wave length of light.
Photodetection of tumours was originally developed in the 1980s with the use of hematoporphyrin derivates such as photofrin. The major limitations of photodiagnosis with these molecules are their low selectivity for cancerous tissues and their capacity to react chemically and induce high photosensitization or necrosis. This latter limitation is, in fact, an advantage in photodynamic therapy, for which these compounds were also proposed.
Folli et al. used a conjugate of an antibody against the carcinoembryonic (CEA) antigen with fluorescein to visualise tumours in patients with colorectal carcinoma (Proc. Natl. Acad. Sci. USA, vol. 89, pp. 7973-7977, 1992). Immunophotodetection of lesions of colon carcinoma LS174T with a conjugate of the anti-CEA MAb 35A7 and indocyanine (Cy5) was demonstrated in a mouse model by Gutowsky et al. (Clin. Cancer Res., vol. 7, pp. 1142-1148, 2001).
However, the clinical utility of these conjugates is rather limited. Conjugates of antibodies with fluorescein possess a rather low excitation and emission wavelength, resulting in low tissue penetration and a substantial degree of nonspecific autofluorescence of the non-cancerous tissues induced by the laser light used for exciting the dye component. The toxicology of Cy5 conjugates is unknown and not yet well-established in the literature.
The present invention addresses these and other associated problems and drawbacks of tumour photodetection. One of the objects of the invention is to provide improved conjugates useful for photodetection of malignant or precancerous tumours which are clinically viable, which overcome one or more drawbacks of the prior art, and which have one or more of the following properties: A high degree of tumour specificity, a high sensitivity such as to allow the detection of very small tumour lesions, good clinical tolerability, high stability, little interference with other dyes, and good manufacturability.
A further object of the invention is to provide improved diagnostic methods for tumours, both in vitro and in vivo, using such conjugates. Used in vivo, such diagnostic methods may be part of novel treatments, such as improved tumour resection methods.
A further object of the invention is to provide methods for preparing such conjugates.
Further objects of the invention will be clear on the basis of the following description of the invention and the patent claims.